Advanced Calculators
Deck Calculator - Calculate Boards, Joists, Posts & Cost
Calculate complete deck materials including decking boards, joists, beams, posts, footings, and hardware. Get accurate estimates with detailed material breakdown and total cost.
Use Deck Calculator - Calculate Boards, Joists, Posts & Cost to get instant results without uploads or sign-ups. Everything runs securely in your browser for fast, reliable output.
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About this tool
Our Deck Calculator is the most comprehensive free tool for estimating materials for deck construction projects. Building a deck requires careful planning and accurate material estimates for multiple components: decking boards, joists, beams, posts, concrete footings, ledger boards, and hardware. This calculator provides a complete materials list for the entire deck structure, from foundation to surface. Whether you're building a simple ground-level platform deck or an elevated deck with stairs and railings, this tool helps you order the right materials and avoid costly mistakes or project delays.
Deck framing is critical for structural integrity and code compliance. The calculator determines joist spacing based on decking board thickness and span - 2×6 boards can span 24" joists, while 5/4 boards need 16" spacing. It calculates the number of joists needed, rim joists for the perimeter, and beam requirements based on joist span and deck width. Post spacing is determined by beam span capacity - typically 6-8 feet for most residential decks. The tool also estimates concrete footings, using the standard rule that footings should extend below frost line depth (typically 3-4 feet in cold climates).
Decking board calculations account for board width, deck dimensions, and installation pattern. Standard 5.5" boards (2×6 nominal) are most common, but 3.5" boards (2×4) and composite boards (various widths) are also supported. The calculator accounts for board end-to-end spacing (typically 1/8" gap for expansion) and determines how many boards of what lengths you need. It includes a 10-15% waste factor for cutting, defects, and mistakes. For diagonal decking patterns, waste increases to 15-20% due to angled cuts.
Cost estimation breaks down expenses by category: decking surface, framing lumber, posts and concrete, and hardware. This helps you see where money goes and identify opportunities to save. The tool is completely free, requires no registration, and works entirely in your browser. Perfect for DIY homeowners planning deck projects, contractors estimating jobs, and anyone needing accurate deck material calculations. All calculations follow building codes and professional deck building standards.
Usage examples
Small Ground-Level Deck
12 ft × 16 ft, 16" joist spacing, 5.5" boards
Boards: 32, Joists: 10, Posts: 6, Concrete: 6 bags
Medium Elevated Deck
16 ft × 20 ft, 16" joist spacing, 4 ft high
Boards: 58, Joists: 15, Posts: 9, Concrete: 18 bags
Large Deck with Diagonal Pattern
20 ft × 24 ft, 16" joist spacing, diagonal boards
Boards: 95 (20% waste), Joists: 18, Posts: 12
Composite Deck
14 ft × 18 ft, 16" joist spacing, composite boards
Boards: 42, Joists: 13, Posts: 8, Hardware: Special fasteners
How to use
- Enter your deck dimensions: length and width in feet
- Select deck board width (typically 5.5" or 3.5")
- Choose joist spacing (12", 16", or 24" on center)
- Specify deck height above ground
- Enter material prices per unit
- View complete material list with boards, joists, posts, and cost
Benefits
- Complete material list for entire deck structure
- Calculates decking boards, joists, beams, and posts
- Concrete footing requirements included
- Support for different board widths and joist spacing
- Diagonal and straight pattern options
- Hardware and fastener estimates
- Cost breakdown by material category
- Code-compliant structural calculations
- Instant results as you adjust dimensions
- Mobile-friendly for on-site planning
- No registration required - completely free
- Based on professional deck builder standards
FAQs
How far apart should deck joists be?
Joist spacing depends on decking board thickness. For 5/4" (1 inch) deck boards, use 16" on center maximum. For 2x (1.5") deck boards, use 16" for most species or 24" for stronger woods. Composite decking manufacturers specify spacing in their instructions (usually 12" or 16"). Closer spacing (12") provides a more solid feel underfoot. Always follow building codes and manufacturer requirements.
How many posts do I need for my deck?
Post placement depends on beam span capacity. For typical residential decks with 2×8 or 2×10 beams, space posts 6-8 feet apart. A 12×16 deck might need 6 posts (2 rows of 3), while a 20×24 deck needs 12 posts (3 rows of 4). Posts must be at corners and support all beam intersections. Heavier loads or weaker lumber require closer spacing. Always check local codes.
What size lumber for deck joists?
Joist size depends on span (distance between beams) and spacing. For 16" joist spacing: use 2×6 for spans up to 8 feet, 2×8 for 8-12 feet, 2×10 for 12-16 feet. For 24" spacing, use one size larger. Southern pine and Douglas fir span farther than SPF (spruce-pine-fir). Maximum spans are specified in building codes - always verify with local requirements.
How deep should deck footings be?
Deck footings must extend below the frost line to prevent heaving. Frost line depth varies by region: 12-18 inches in warm climates, 3-4 feet in northern climates, 4-6 feet in Alaska/Canada. Minimum footing diameter is 12 inches, but 16-18 inches is better for stability. Use 50-80 pounds of concrete per footing. Install post bases above grade to prevent wood rot.
How much does it cost to build a deck?
DIY material costs: pressure-treated wood decks $15-25 per square foot, cedar $25-35/sq ft, composite $30-45/sq ft. A 12×16 deck (192 sq ft) costs $2,880-8,640 in materials. Professional installation adds $15-35/sq ft ($2,880-6,720 labor). Total costs: $5,760-15,360 professionally built. Stairs, railings, and built-in features add 20-50%. DIY saves 50-60% but requires skills, tools, and time.
What is the best wood for decks?
Pressure-treated pine is most economical ($2-3/sq ft) and lasts 15-20 years with maintenance. Cedar and redwood are naturally rot-resistant ($4-6/sq ft), lasting 20-30 years. Tropical hardwoods (ipe, cumaru) are extremely durable ($7-10/sq ft), lasting 25-50 years. Composite decking ($5-10/sq ft) is low-maintenance and lasts 25-30 years but costs more upfront. Choose based on budget, aesthetics, and maintenance preference.
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